The invention relates to a process for the production of non-woven material from endless filaments which are drawn off from spinnerets in the form of a warp by means of a gaseous propellant and are deposited, after moving through a tube-like filament draw-off device, on a substrate for the formation of the non-woven material. To obtain a desired filament draw-off force, the gaseous propellant is supplied to a filament draw-off nozzle, located at the input side of the filament draw-off device, with a set input pressure (compressed air pressure) and with a set input volume (amount of compressed air). Furthermore, the invention relates to an apparatus for the carrying out of the process.
Processes and apparatus of the species mentioned above are known from German Pat. No. 1 785 158, British Pat. No. 1 282 176 and British Pat. No. 1 297 582. There a warp coming from a liquefied material and through spinnerets is guided through a filament draw-off device having a filament draw-off nozzle at its upper end. The latter is fed with highly compressed air.
The so-called Lavalle enlargement adjoins the narrowest annular slit of the filament draw-off nozzle at the exit of which low pressure is generated. This low pressure then also occurs via a small inner filament-guide at the input side of the filament draw-off nozzle and makes possible the threading of the warp.
A filament offlet with an inner diameter of the Lavalle enlargement adjoins the Lavalle enlargement, into which air flows at supersonic speed. After about half the distance of the filament offlet of a total length of approximately 250 mm a compression shock with following subsonic flow occurs, which further slows inside the adjoining filament guide tube having a four- to six-fold diameter.
Within the filament draw-off device consisting of the filament offlet and the filament guide tube the drawing of the filaments takes place, which thereby become thinner. A substantial part of the filament draw-off force is provided by the filament offlet. The object of the filament guide tube is only to transport the warp to a spreading extruder and, if required, to so-called Coanda shells, in order to distribute the filaments evenly and to spread them before they are deposited on a substrate for the formation of the non-woven material.
It is customary for obtaining large-area widths of nonwoven material to dispose a plurality of filament draw-off devices side-by-side, wherein the separate draw-off nozzles are in each case fed with highly compressed air as the gaseous propellant. The process this far known and described, although effective in practical use, is nevertheless not free of disadvantages. The compressed air energy necessary for drawing of the filaments represents a considerable cost factor which inevitably is reflected in the end price of the non-woven material.
Even though it could be considered to diminish the cost factor for the energy needed by reducing the compressed air energy, this measure cannot be taken, since then the required filament draw-off force and the required drawing for the production of a perfect non-woven material are no longer available. For this reason, highly compressed air has to be relied on to obtain an optimal filament draw-off force and an optimal drawing.